Physicians frequently make use of catheters today in medical procedures to gain access into interior regions of the body. In some procedures, the catheter carries an energy emitting element on its distal tip to ablate body tissues.
In such procedures, the physician must establish stable and uniform contact between the energy emitting element and the tissue to be ablated. Upon establishing contact, the physician must then carefully apply ablating energy to the element for transmission to the tissue.
The need for precise control over the emission of ablating energy is especially critical during catheter-based procedures for ablating heart tissue. These procedures, called electrophysiology therapy, are becoming increasingly more widespread for treating cardiac rhythm disturbances, called arrhythmias.
Today, cardiac ablation procedures typically use radiofrequency (RF) energy to form a lesion in heart tissue.
Conventional cardiac ablation systems designed to cure re-entrant supra ventricular tachycardia (SVT), often create lesions in myocardial tissue with a penetration depth of about 3 to 5 mm and a lesion volume of less than 0.2 cm.sup.3, depending upon the size of the electrode and the amount of power that is applied.
However, to consistently cure MVT by ablation, a penetration depth greater than 3 to 5 mm and a lesion volume of at least 1 cm.sup.3 is estimated to be required.
The solution may lie in larger electrodes and higher power systems. Yet, implementing this solution may itself pose additional problems.
The amount of RF energy that must be conveyed to conventional electrodes to create even small therapeutic lesions is already quite high (upwards to 50 watts or more). This is because conventional RF emitting electrodes are very inefficient. Only about 25% of the RF energy delivered to the electrode is actually directed into the heart tissue. The rest of the RF energy is dissipated into the circulating blood pool within the heart.
As a result, finding a predictable relationship between required RF power input and lesion volumes is often problematic. Not only are the power output to input efficiencies quite low, but they are also highly variable among patients.
Furthermore, the delivery of even larger amounts of RF energy to conventional electrodes means the dissipation of even larger amounts of energy into the blood pool. The effects of local blood heating, like the creation of thrombotic emboli, become more pronounced.
There is a need for energy emitting electrodes that more uniformly direct larger amounts of energy into the tissue, and not into the surrounding blood pool.
There is also a need for energy emitting electrodes that require less input power to create therapeutic lesions, regardless of their size.